The use of silver in products or dressings for wound care has been known for a long time. One knows especially of dressings in the form of bandages or compresses for local application, of which all or part is impregnated with a compound capable of delivering silver ions to the wound. Silver is thus used as an antimicrobial agent. The action of the silver can be completed by anti-odorants or humidity regulators. Silver dressings are available today in a wide variety of forms, common to modern wound care products. That is, the dressing or bandage can be a fabric structure employing woven or non-woven fiber layers (such as Smith & Nephew Acticoat or Johnson & Johnson's Actisorb), or a polymer thin film sheet, or a foam pad, or an absorptive filler dressing (such as Convatec Aquacel AG). Likewise, the silver ions can be delivered in various forms, via metallic silver, silver nano-particles, silver zeolite, silver chloride, etc. Typical dressings are multi-layer structures, with different properties relative t absorbency, moisture vapor transmission, oxygen transmission, bacterial and water barrier functionality, adhesion, and other factors, provided in the different layers. The layers are used for the physical properties that their structure provides, or serve as reservoirs of chemicals.
Various compounds containing silver ions can be used to fight against wound contamination. For example, resins incorporating silver, such as zeolites, can be used in wound dressings, as described in U.S. Pat. No. 4,775,585. Other compounds based on glass or other compounds such as carbon fibers or cellulose polymers can be used. These are for example resins, zeolites, compounds based on glass or other compounds such as carbon fibers or cellulose polymers. These compounds are capable of delivering the silver in a controlled way, and spreading it on the wound.
Various modern wound dressings are available today that provide transparency to the wound site, so that the wound can be visually inspected without direct contact by the clinician. For this reason, transparent polymer thin film dressings are frequently used, either for dry wounds or lightly exuding wounds, or as a secondary dressing, as appropriate. As an example, visual wound inspection allows the clinician to monitor wound development, including regular measurement of their dimensions, and in particular their circumference. Otherwise, these measurements, mostly made using a tape measure, can only be taken by releasing the wound from its dressings. This operation is made delicate by the fact that the wound is then unprotected.
Among the numerous silver dressings presently offered, the Arglaes Film Dressing is the only one marketed with optical transparency as an attribute. The dressing utilizes a technology described in U.S. Pat. No. 5,470,585 which incorporates the silver into a water-soluble glass. This glass, which comprises a furnace-fused complex of calcium and sodium phosphates including a silver-salt, was principally designed to provides a slow-release of silver ions, enabling a dressing to have anti-bacterial properties over an extended time period of up to a week. Optical transparency is a secondary attribute of this dressing, which can degrade during use, as the silver reacts to light and turns gray.
Dressing or bandage transparency could be useful for enabling light therapy treatment of a wound without causing undue disruption of the wound site. Subjecting wounds to light and in particular to light in the red and/or near-infrared spectrum is indeed known as a way of accelerating the healing of wounds. Light has a stimulating action on the metabolism of cells in damaged tissues inside the wound and so favors their repair. This has the effect of accelerating healing and even of repairing chronic wounds where conventional treatments are ineffective. For information one can refer to “Primary and secondary mechanisms of action of visible to near-IR radiation on cells” of Tiina Karu in J. Photochem. Photobiol. B: Biol 49 (1999), pages 1-17.
There is then a need for an improved silver dressing or bandage that provides improved optical transmission, including in the near infrared spectra, as well as improved anti-bacterial efficacy.
Other background art can be found in: US 2005/0037058; WO2004/039724; WO2004/009494; “Current trend using antimicrobial agents-Topics related to inorganic disinfectants” by Yoshinobu Matsumura in Bioscience and Industry, vol 60(2), 89-94 (2002); U.S. Pat. No. 4,728,323; U.S. Pat. No. 5,556,699; U.S. Pat. No. 5,888,711; U.S. Pat. No. 6,027,702; and U.S. Pat. No. 6,620,397.
In the context described above, the invention highlights a need to have transparent dressings. It also highlights a technical incompatibility of this need with the use of effective metal-based antimicrobial agents.
Transparency of the dressing is sought to be able to observe the wound and measure it, without having to remove the dressing. This facilitates monitoring of the wound's development. Furthermore, transparency enables the wound to be subjected to light radiation treatment, still without removing the dressing.
The property of transparency however is generally incompatible with the use of known silver-based antimicrobial agents. Indeed, silver-based compounds have insufficient transparency at thicknesses useful for viewing or irradiating wounds. Blackening of the silver, either by light activity or chemical reaction with the tissue, during the use of the dressings, can further reduce the transparency. For example, silver chloride and silver nitrate, are optically active silver forms, that change their transparency upon exposure to light.